The present invention relates to an optical disk drive and, particularly, to an optical disk drive having a focus control function as well as a tracking control function.
In an optical disk drive of an optical recording and reproducing apparatus, an amount energy of laser light emitted from a laser during an information recording mode operation is in the order of 10 times that during an information read mode operation. Therefore, a focus error detecting circuit for detecting a focus error of a laser light and a track error detecting circuit for detecting a track error of the laser light of the optical recording and reproducing apparatus, which are adjusted in gain to the information read mode operation, are used in the information recording mode operation, these detecting circuits may be saturated and servo gains thereof may be fluctuated. On the other hand, when a focus error detecting circuit for detecting a focus error of a laser light and a track error detecting circuit for detecting a track error of the laser light of the optical recording and reproducing apparatus, which are adjusted in gain to the information recording mode operation, are used in the information read mode operation, these detectors could not operate appropriately. In order to make the focus error detecting circuit and the track error detecting circuit operable appropriately in both the information recording mode operation and the information read mode operation, a gain switching function has been provided in each of them so that loop gains of this control system can be regulated.
U.S. Pat. No. 4,023,033 discloses an example of the focus error detector and U.S. Pat. No. 4,989,193 discloses an example of the track error detector. A gain switching operation of the focus error detector of U.S. Pat. No. 4,023,033 or of the track error detector of U.S. Pat. No. 4,989,193 is performed at a start time and at an end time of the information recording operation. In such case, there may be a case where spiked offset are generated on a focus error signal and a track error signal, depending upon a circuit delay. Further, there may be a case where spiked noise from a peripheral circuit is mixed in the focus error signal and/or the track error signal. When a focus and/or tracking servo operation is performed on the basis of an input signal mixed with such spiked noise, an objective lens of the optical information recording and reproducing apparatus may be accelerated too much, resulting in off-track and/or off-focus.
In order to prevent such off-focus and/or off-track, it is desired that the servo control system is not sensitive to such spiked noise. In order to realize this, a servo frequency band in a conventional optical recording and reproducing apparatus is set to a value lower enough than a frequency band of the spiked noise.
On the other hand, with the recent development of technology, it has been requested to increase an information recording speed as well as an information read speed of an optical recording and reproducing apparatus. This means that there is a tendency of increase of rotation speed of a recording medium, and the servo frequency band should be increased. In order to make the servo system insensitive to the spiked noise having high frequency components in increasing the frequency of the servo system servo frequency band, any new measure should be provided. However, there is no such measure proposed as yet.
As mentioned, in the conventional technology, it is usual in order to make the servo system insensitive to the spiked noise containing high frequency components to set the frequency band of the servo system low. However, since the frequency band of the existing servo system is increased in order to improve the information recording and reading speed, the servo system responds to the spiked noise containing high frequency components and these may be the off-focus and/or off-track. In the situation of the off-track, the laser beam may scan other tracks than an aimed track.